Hydrogenation catalysts can be used to hydrogenate the acetylene content of a given feedstream to ethylene. An acidic zeolite catalyst can then be used to convert ethylene to useful and commercially viable gasoline range hydrocarbons, or C.sub.5 + liquid products. The original feedstream often, however, contains excess hydrogen and ethylene which hinder the selective conversion of acetylene to ethylene, instead converting the feedstream to ethane. A hydrogenation catalyst which operates efficiently in the presence of excess ethylene and hydrogen, eliminating the problem of feedstream conversion to ethane, would be advantageous.
The hydrogenation of acetylene to ethylene is a known process for the removal of small amounts of acetylene from ethylene feedstocks. Typically, highly dispersed palladium on a medium surface area support is used. Hydrogen is either added in stoichiometric amounts or in a slight molar excess and the gas is treated until complete hydrogenation of acetylene occurs. The feedstock, however, often contains both acetylene and ethylene, therefore requiring that the catalyst be selective for the hydrogenation of acetylene to ethylene over the hydrogenation of ethylene to ethane. Stoichiometric hydrogen to acetylene ratios are often used in conjunction with acetylene selective catalysts to ensure that feed ethylene is not hydrogenated to ethane, as well as that the ethylene produced from acetylene hydrogenation is not further hydrogenated to ethane. Catalysts which are selective in the presence of excess hydrogen have been documented. Most often, however, the selectivity of these catalysts is achieved by intentionally poisoning the catalysts with a variety of substances which impart selectivity. The poison is added to the feed gas in low concentration and must be present throughout the reaction in order for high selectivity to be maintained.
U.S. Pat. No. 3,308,180 discloses a process for the separation of acetylene from a feedstream containing both acetylene and ethylene by selective hydrogenation with a catalyst containing 0.01 to 0.1 wt % palladium on an alumina support.
U.S. Pat. No. 3,325,556 discloses a process for the selective hydrogenation of acetylene in an acetylene/ethylene-containing mixture by the addition of carbon monoxide to this mixture and treatment thereof with an excess of hydrogen at elevated temperature and pressure in the presence of a catalyst comprising a noble metal disposed on alumina.
Palladium zeolite catalysts used to selectively hydrogenate acetylene in the presence of ethylene were reported by W. L. Kranich et al., Applied Catalysis, 13 (1985), 257-267.
U.S. Pat. No. 4,387,258 relates to the selective hydrogenation of unsaturated hydrocarbon feeds using catalysts comprising a catalytically-active metal on a crystalline silica support.
Catalysts of the zeolite variety used for treatment of olefinic gasoline are disclosed in U.S. Pat. Nos. 4,211,922; 4,277,992; 4,260,839; 4,450,311; 4,456,779; and 4,511,747.
International Application PCT/US85/00770 discloses a catalyst system useful for converting an ethylene-containing feedstock to heavier hydrocarbons in the gasoline or distillate boiling range. The system involves passing the feedstock over a siliceous crystalline molecular sieve to convert ethylene to C.sub.3 -C.sub.4 olefins and C.sub.5 + hydrocarbons, separating the olefins and C.sub.5 + hydrocarbons, and then passing the olefins over a second siliceous molecular sieve to obtain heavier hydrocarbons.
What is lacking in the art, however, is a hydrogenation catalyst operative for the conversion of acetylene to ethylene, from a feedstream containing a relatively high ratio of acetylene to ethylene, such as 0.1 or greater, in the presence of ethylene and excess hydrogen. Also lacking is a single-pass conversion process using such a hydrogenation catalyst in conjunction with an acidic zeolite catalyst for the conversion of an acetylene-, ethylene- and hydrogen-containing feedstream to gasoline range hydrocarbons.
It is an object of the present invention, therefore, to develop a process for treating an acetylene hydrogenation catalyst to impart greater selectivity for acetylene to ethylene conversion to the catalyst when used in the presence of ethylene and excess hydrogen.
It is a further object of the present invention to provide a single-pass process which uses the pretreated hydrogenation catalyst in conjunction with an acidic zeolite catalyst to convert an acetylene-, ethylene- and hydrogen-containing feedstream to gasoline range hydrocarbons.
Other objects, aspects and advantages of the present invention will be apparent to those skilled in the art upon consideration of the following description of this invention and of the appended claims.